1. Field of the Invention
The present invention relates to an optical pointing device and, more particularly, to an image sensor, an optical pointing device and a motion calculating method of the optical pointing device which can calculate larger motion of the optical pointing device for an X axis direction.
2. Description of the Related Art
In general, an image sensor gets a surface image and provides an image processing device with the surface image. The image processing device which employs the image sensor includes, for example, a digital camera and an optical pointing device.
The field in which the present invention concerns is an image sensor which is employed in an optical pointing device which obtains a surface image rapidly through the image sensor and compares the currently obtained surface image with the previously obtained surface image to calculate a motion value.
FIG. 1 is a schematic view illustrating a conventional image sensor. The image sensor 1 includes a square-shaped pixel array in which the number (12) of pixels which forms an X axis and the number (12) of pixels which forms a Y axis are identical to each other. Each pixel 2 includes a photo diode 2a that an X-axis pitch X PITCH is identical to a Y-axis pitch Y PITCH, where the X-axis pitch X PITCH is identical in value to the Y-axis pitch Y PITCH. That is, each pixel has a square shape.
Each pixel 2 collects incident light while a shutter is in an ON state and generates an electrical signal corresponding to quantity of the collected light. The image sensor 1 provides an internal circuit of the optical pointing device with an image of a surface in the form of 12×12 electrical signals which are generated from the respective pixels. That is, the image sensor 1 provides the internal circuit of the optical pointing device with the image of the surface that an X-axis length “b” and a Y-axis length “a” are identical.
The internal circuit of the optical pointing device obtains the surface image collected during a current sampling period using the 12×12 electrical signals supplied from the image sensor 1 and compares it with the previously obtained surface image to thereby calculate a motion value of the optical pointing device.
FIGS. 2 and 3 are schematic views illustrating a motion calculation method of the optical pointing device which employs the image sensor of FIG. 1.
In FIG. 2, a frame 11 is a previous surface image obtained through the image sensor of FIG. 1 during a previous sampling period, and a frame 12 is a current surface image obtained during a current sampling period.
In order to calculate a motion distance during the current sampling period, the optical pointing device sets the previous frame 11 obtained during the previous sampling period as a reference frame, and sets a central area of the reference frame 11 as a reference area 11a, and sets the current frame 12 obtained during the current sampling period as a sample frame.
As shown in FIG. 3, the reference area 11a is zigzag-scanned from a left top portion (−3,3) of the sample frame 12 to a right bottom portion (3,−3) in one pixel unit to thereby calculate correlation between the reference area 11a and the sample frame 12.
A location of the sample frame 12 having the highest correlation is obtained, and a motion value of the optical pointing device is calculated using the location of the obtained sample frame 12.
In FIG. 3, the sample frame 12 has the highest correlation with the reference area 11a at a location (0,3), and thus a resultant motion value of the optical pointing device is (0,3) PIXEL.
As described above, the conventional optical pointing device gets motion by comparing the surface images continuously collected by the image sensor. An image collection rate, i.e., sampling rate is basically set to be fast in consideration of fast motion. The commercially available optical pointing device usually samples the surface image more than 1,500 times per second.
The optical pointing device is moved by a human, and the human moves more frequently in the X axis direction than in the Y axis direction and, thus a motion value of the X axis direction is greater. Thus, the sampling rate of the optical pointing device depends on the motion for the X axis direction, and so the fast sampling rate is needed as described above.
The optical pointing device and the keyboard are placed side by side for the user's convenience. In the currently available keyboard, the X axis is longer than the Y axis, and also the X axis is longer than the Y axis in the motion area of the optical pointing device for moving a cursor on the monitor screen. Therefore, in most cases, the length of the X axis on which the keyboard and the optical pointing device are placed is longer than the X axis of the monitor screen.
Further, for the user's convenience, a location of the optical pointing device protrudes to the right side of the keyboard to match the user's eyes with the center of the hand. Such keyboard and optical pointing device have more area for the X axis.
This may cause inconvenience to the user when the user uses a computer in a limited area such as a train or airplane. That is, there is a problem in that the motion area of the optical pointing device is limited.